Apparatus for photolithography process with gas-phase pretreatment

ABSTRACT

The present invention discloses an apparatus for photolithography process with phase-pretreatment. The apparatus comprises several chambers: a vapor prime chamber, a vacuum-bake chamber, a chill-plate chamber, a coater chamber and a stepper chamber. Further, an interface chamber is between the stepper chamber and the apparatus. These chambers are connected together to a track system. A base gas is introduced into one of these chambers to perform a gas-phase pretreatment. The concentration of the base gas can be controlled and the processing time of the pretreatment process is well controlled by operating the apparatus. As a photoresist layer is applied on a substrate, the photoresist layer is hardened in the base gas to increase the depth of focus in photolithography process.

FIELD OF THE INVENTION

The present invention relates to an apparatus for a deep ultra-violet(DUV) photolithography process, and more specifically, to an apparatusfor the gas-phase pretreatment of a photoresist.

BACKGROUND OF THE INVENTION

According to the development of integrated circuits, the line-width ofultra-large-scale integrated circuit is smaller than one quarter micronmeters. A traditional photolithography process is performed for to theformation of quarter-micron-meters lines in integrated circuits but asingle line is narrower than one quarter micron meters. In thetraditional deep ultraviolet (DUV) photolithography process, anisolated-line pattern has a smaller depth of focus (DOF) than that adense-line pattern has. Some approaches are tried to solve the aboveissue for the isolated-line pattern.

A next-generation DUV stepper machine uses a kind of light, which has awavelength about 0.193 nanometers, to expose photoresist. At the recentyears, the DUV stepper machines, which are popular used in factories,use light that has wavelength about 0.248 nanometers. Using thenext-generation stepper machine, the DOF of the isolated line patternmust be increased. Nevertheless, the new stepper machine can not developultra-violet photoresist pattern very well.

Other approach to increase the DOF of the integrated circuits is to usea phase-shifting mask during a photolithography process. Aphase-shifting mask (PSM) is consisted of several masking layers andattenuated layers. The phase-shifting mask has a special structure inorder to generate an electrical field, which has a good contrast, beingapplied on the mask when the light of a stepper machine transmits themask. However, the cost for manufacturing a phase-shifting mask is soexpensive. Thus, the phase-shifting mask is not popularly adapted inwafer factories. Additionally, sub-resolution assisted features areplaced around an isolated line on a mask so that the DOF of the isolatedline could be increased. Nevertheless, to fabricate the assistedfeatures on a mask needs complex calculations and designs. So, thisapproach is not available for semiconductor's factories.

A surface pretreatment is used to harden the surface of a DUVphotoresist layer. Conventionally, the surface pretreatment "isperformed by using DI water or developer" and it is named as aliquid-phase pretreatment. In a liquid-phase pretreatment, thephotoresist layer is dipped in DI water or developer before thedeveloping process of the photoresist layer. But, the liquid-phasepretreatment is rough to the DUV photoresist layer. The profile of theDUV photoresist for defining an isolated line, which is exposed, has a"T-shape" to "cross section after the liquid-phase pretreatment". As theisolated-line DUV photoresist layer has a T-shape cross section, thecritical dimension of the DUV photoresist can not be definitelydetermined. Moreover, the liquid-phase pretreatment is not uniformenough. Referring to FIG. 1, a cross section's view of a photoresistlayer 10 not being treated is shown. In spite of the photoresist layer10 has a sharp profile but the top surface of the photoresist layer 10are round and the critical dimension of the isolated line under thephotoresist layer 10 will be hard to control during following etchingprocesses. Referring to FIG. 2, a cross sectional view of a DUVphotoresist layer 10, which is treated by using a liquid-phasepretreatment and is developed, is shown and it has a T-shape crosssection.

According to the above discussion, a new surface pretreatment for theDUV photoresist is needed to increase the DOF of an isolated-linepattern.

SUMMARY OF THE INVENTION

A deep ultra-violet (DUV) track system according to the presentinvention is disclosed. The track system comprises indexer end station,a vapor-prime chamber, chill-plate chambers, a coater chamber,vacuum-bake chambers, a stepper chamber and a develop chamber. A basegas is introduced into on of these chambers and the concentration of thebase gas is well controlled by operating the track system. In addition,the processing time of the base gas introduced into the track system iscontrolled, too. The functions of these chambers are described as below.

The indexer end station is used for storing a substrate. The vapor-primechamber connected to the indexer end station, the substrate is heatedand a chemical hexamethyldisilizane (HMDS) is applied on a surface ofthe substrate in the vapor-prime chamber.

The chill-plate chambers connected to the vapor-prime chamber forbringing the substrate to a stable, constant temperature.

The coater chamber connected to the chill-plate chamber for uniformlycoating a photoresist layer on the substrate. The vacuum-bake chambersconnected to the coater chamber for heating the photoresist layer.

The stepper chamber connected to the vacuum-bake chamber through aninterface chamber and the photoresist layer is exposed in the stepperchamber.

The developer chamber connected to the chill-plate chamber and exposedor unexposed portion of the photoresist layer is removed in theenveloper chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated as the same becomesbetter understood by reference to the following detailed description,when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 shows a profile of a photoresist layer, which is exposed and thendeveloped without any pretreatment before exposed in accordance withprior art;

FIG. 2 shows a profile of a photoresist layer, which is exposed and thendeveloped with a liquid-phase pretreatment before it is exposed inaccordance with prior art;

FIG. 3 shows the relation between a depth of focus of an isolated-linepattern and an energy latitude of a photolithography process for formingthe isolated-line pattern in accordance with prior art;

FIG. 4 shows the relation between a depth of focus of an dense-linepattern and an energy latitude of a photolithography process for formingthe dense-line pattern in accordance with prior art;

FIG. 5 shows a flow of a lithography process including the coating, thebake, the exposure and the chill of a photoresist layer in accordancewith the present invention;

FIG. 6 is a top view of a lithography machine including several chambersin accordance with the present invention;

FIGS. 7A-7I shows a cross section view of a substrate, a photoresistlayer is patterned on the substrate by using a lithography process inaccordance with the present invention;

FIG. 8 shows the relation between a depth of focus of an isolated-linepattern and an energy latitude of a photolithography process for formingthe isolated-line pattern in accordance with the present invention;

FIG. 9 shows the relation between a depth of focus of an dense-linepattern and an energy latitude of a photolithography process for formingthe dense-line pattern in accordance with the present invention; and

FIG. 10 shows the profile of a photoresist layer, which is exposed andthen developed with a gas-phase pretreatment before the photoresistlayer is exposed in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention discloses photolithography track system havingseveral reacting chambers to perform a photolithography process fordefining a photoresist layer on a substrate. A base gas can beintroduced into one of the reacting chambers for a gas-phasepretreatment process of photoresist material. In the track system, theconcentration of the base gas can be controlled and the processing timeof the pretreatment process is determined by operating the track system.The gas-phase pretreatment is performed in the photolithography machine,such as a track system, to harden the surface of photoresist. In thefollowing description, a process to define a pattern on a substrate willbe explained.

Firstly, thin film 200 is deposited on the substrate 100, as shown inFIG. 7A. The thin film 200 will be patterned in a photolithographyprocess. Referring to FIG. 7B, a pre-bake or prime process is performedon the surface of the thin film 200. The pre-bake process is used toensure good photoresist adhesion by removing moisture from the surfaceof the wafer and is performed by heating the wafer caused the moistureto evaporate from the surface. Besides, the prime process is used to aidin the adhesion of photoresist. A chemical hexamethyldisilizane (HMDS)is used to promote adhesion of the photoresist to the surface of thewafer. HMDS is applied to the heated wafer by introducing nitrogensaturated with HMDS vapor into the vapor prime oven chamber. Then, achill process is performed to bring the substrate 100 to a stable,constant temperature before applying photoresist. The chill process isperformed in a chill plate of a track system.

Referring to FIG. 7C, a photoresist layer 300 is coated onto the surfaceof the thin film 200. Typically, the photoresist layer 300 is deepultraviolet (DUV) photoresist. Referring to FIG. 7D, a soft-bake processis used to dry the photoresist layer 300 by removing most, but not all,of the solvent. Evaporating the solvent converts the photoresist layerto a mechanically stable film. The soft-bake process is performed in avacuum bake chamber of the track system. After the soft-bake process, achill process is used again to bring the substrate 100 to a stabletemperature.

Referring to FIG. 7E, UV light transmits a reticle 400 to transfer animage from the reticle to the photoresist layer 300, the reticle 400 isaccurately aligned and focused to the substrate 100. After the exposureof the photoresist layer 300, a post-exposed bake is performed tostabilize the photoresist, specifically to the exposed and unexposedareas of the photoresist layer 300. A third chill process is used tobring the substrate 100 to a stable, constant temperature beforeapplying the developer solution. The post-exposed bake and the thirdchill process are performed in a vacuum bake chamber and on a chillplate of the track system, respectively.

Referring to FIG. 7F, a develop process is performed to removes theunwanted portion of the photoresist layer 300 by using a developersolution. It is noted that positive photoresist developer removes theexposed photoresist coating and negative photoresist developer removesunexposed photoresist coating. In some processes, a visual inspection(develop check) is done to identify defects in the photoresist layer300. Critical dimensions (CDs) of the photoresist layer 300 aremeasured, and an alignment check may also be done.

Referring to FIG. 7G, the substrate 100 is baked in the vacuum chamberor a hot-plate chamber to remove moisture from the wafer surface andharden the pattern of the photoresist layer 300. The process to bake thesubstrate 100 after the developing process is indicated as a hard bakeprocess. The substrate 100 is then chilled on a chill plate of the tracksystem to cool the wafer before transferring it back to the indexercassette.

Referring to FIG. 7H, the thin film 200 is etched by using thephotoresist layer 300 as an etching mask. The etching process to etchthe thin film 20 is a dry or wet etching. After the etching process, apattern is formed in the thin film 200. Lastly, the photoresist layer300 is stripped, as shown in FIG. 7I.

The gas-phase pretreatment of the photoresist layer 300 is inserted intothe above process flow. The gas-phase pretreatment could be performedbefore the developing process that is shown in FIG. 7F. That is, thegas-phase pretreatment can be done before or after the exposure of thephotoresist layer 300, to harden the surface of the photoresist layer300. The gas-phase pretreatment is performed in an ambient of base gas.In a preferred embodiment, the base gas is amine (NH₄ OH) gas or a gashaving a pH value between about 7.1 and 13, which has a temperaturebetween about 15 and 250 centigrade degrees, a concentration betweenabout 10⁻³ ppm and 10 mole/cm³. In a case, the processing time of thegas-phase pretreatment is between about 1 and 120 seconds.

Referring to FIG. 5, a process flow of a photolithography process isshown. A wafer is took out from an indexer end station 500 and enters avapor prime chamber 516. In the vapor prime chamber 516, the wafer isbaked, as shown in FIG. 7B. The wafer is then putted on a chill plate ina chill pate chamber 528 to cool the wafer down. After the pre-bake andchill process, photoresist is coated in a coating chamber 530 by usingspin-on. The coating of the photoresist is shown in FIG. 7C. Afterwards,the wafer enters a vacuum-bake chamber 524 and a soft-bake process isperformed in the vacuum-bake chamber 524. The wafer is then cooled downon a chill plate in a chill-plate chamber 522.

The photoresist is exposed through a reticle to transfer a pattern tothe photoresist. The exposure process is done in a stepper chamber (notshown). After the expose process, the wafer leaves the track system andenters into an interface chamber (not shown) between the stepper chamberand the track system through a shuttle 600, and the wafer then entersinto the track system. Afterwards, a post-expose bake process isperformed and a chill process is done to bring the wafer to a stabletemperature, as shown in the FIG. 7E. The post-expose bake and the chillprocess are done in a vacuum bake chamber 512 and in a chill-platechamber 514, respectively.

A develop process, as shown in FIG. 7F, is performed in a developerchamber 526. Then, the wafer is putted on a hot plate in a hot-platechamber 518 to harden the photoresist and to remove moisture of thephotoresist. Finally, a chill process is performed in anindexer-end-station chill chamber 530. After the final chill process,the wafer returns the indexer end station (IES) 500.

The gas-phase pretreatment could be performed in the vapor-prime chamber516, vacuum-bake chamber 524, chill-plate chamber 528, 514, interfacechamber or stepper chamber. The base gas for the gas-phase pretreatmentis introduced into the module or chambers, which is used to control aprocessing condition, such as the temperature and concentration of thebase gas. Besides, the processing time of the gas-phase pretreatmentmust be well controlled, too.

Referring to FIG. 6, a top view of the track system is shown. The tracksystem comprises several chambers, like the vacuum-bake chambers 512,524, chill-plate chambers 514, 528, 522, vapor-prime chamber 516,hot-plate chamber 518, developer chamber 526, coater chamber 530,indexer end stations 500, IES-stage chamber 510 and IES-chill chamber530. In addition, these chambers are connected together for performing aphotolithography process of wafers. A stepper chamber (not shown) isattached with the track system and wafers are transferred from the tracksystem to the stepper chamber through a shuttle and several indexer endstations 500 are attached with the track system. Several shuttles 600are placed between the chambers for transferring wafers.

Referring to FIGS. 3 and 4, the relation of the energy latitude to thedepth of focus (DOF) of an isolated-line pattern and an dense-linepattern without any pretreatment is respectively shown. Referring toFIG. 8, the relation of the energy latitude with the DOF of anisolated-line pattern with a gas-phase pretreatment, which is mentionedin the present invention, is shown. A relation of energy latitude to theDOF of a dense-line pattern being treated by using the gas-phasepretreatment is shown in FIG. 9. The DOF of an isolated-line patternbeing treated by using the gas-phase pretreatment is larger than thatnot being treated. The DOF of an dense-line pattern being treated byusing a gas-phase pretreatment is as large as the DOF of an dense-linepattern not being treated by using any surface treatment. Thus, toperform a gas-phase pretreatment on a photoresist could increase the DOFof an isolated-line pattern during the photolithography process, and theDOF of an dense-line pattern is not changed.

Referring to FIG. 10, a cross sectional view's of a photoresist layer10, which is treated by using the gas-phase pretreatment, is shown. InFIG. 10, the photoresist layer 10 has a sharp and planar profile, whichis easy to being aligned and to control the critical dimension of apattern under the photoresist layer 10 during etching process. Theprofile according to FIG. 10 differs from the profile according to FIG.1 and FIG. 2. It means that the gas-phase pretreatment could improve theprofile of the photoresist layer after developing process.

While the preferred embodiment of the invention has been illustrated anddescribed, it will be appreciated that various changes can be madetherein without departing from the spirit and scope of the invention.

What is claimed is:
 1. A deep ultra-violet (DUV) track system, said system comprises:an indexer end station for storing a substrate; a vapor-prime chamber connected to said indexer end station, wherein said substrate is heated and a chemical solution is applied on a surface of said substrate in said vapor-prime chamber before a photoresist layer is coated on said substrate, a base gas being introduced into said vapor-prime chamber to harden a surface of said photoresist layer; at least one chill-plate chamber connected to said vapor-prime chamber for bringing said substrate to a stable, constant temperature; a coater chamber connected to said chill-plate chamber for uniformly coating said photoresist layer on said substrate; at least one vacuum-bake chamber connected to said coater chamber for heating said photoresist layer; a stepper chamber connected to said vacuum-bake chamber through an interface chamber, wherein said photoresist layer is exposed in said stepper chamber; and a developer chamber connected to said chill-plate chamber, wherein exposed or unexposed portion of said photoresist layer is removed in said developer chamber.
 2. The track system according to claim 1, wherein said base gas introduced into said vapor-prime chamber has a concentration between about 10⁻³ ppm and 10 mole/cm³.
 3. The track system according to claim 1, wherein said base gas has a pH value between 7.1 and 13°.
 4. The track system according to claim 1, wherein said base gas introduced into said vapor-prime chamber has a temperature between about 15 and 250 centigrade degrees.
 5. A deep ultra-violet (DUV) track system, said system comprises:an indexer end station for storing a substrate; a vapor-prime chamber connected to said indexer end station, wherein said substrate is heated and a chemical solution is applied on a surface of said substrate in said vapor-prime chamber before a photoresist layer is coated on said substrate; at least one chill-plate chamber connected to said vapor-prime chamber for bringing said substrate to a stable, constant temperature and a base gas being introduced into said chill-plate chamber to harden a surface of said photoresist layer; a coater chamber connected to said chill-plate chamber for uniformly coating said photoresist layer on said substrate; at least one vacuum-bake chamber connected to said coater chamber for heating said photoresist layer; a stepper chamber connected to said vacuum-bake chamber through an interface chamber, wherein said photoresist layer is exposed in said stepper chamber; and a developer chamber connected to said chill-plate chamber, wherein exposed or unexposed portion of said photoresist layer is removed in said developer chamber.
 6. The track system according to claim 5, wherein said base gas introduced into said chill-plate chamber has a concentration between about 10⁻³ ppm and 10 mole/cm³.
 7. The track system according to claim 5, wherein said base gas has a pH value between about 7.1 and
 13. 8. The track system according to claim 5, wherein said base gas introduced into said chill-plate chamber has a temperature between about 15 and 250 centigrade degrees.
 9. A deep ultra-violet (DUV) track system, said system comprises:an indexer end station for storing a substrate; a vapor-prime chamber connected to said indexer end station, wherein said substrate is heated and a chemical solution is applied on a surface of said substrate in said vapor-prime chamber before a photoresist layer is coated on a surface of said photoresist; at least one chill-plate chamber connected to said vapor-prime chamber for bringing said substrate to a stable, constant temperature; a coater chamber connected to said chill-plate chamber for uniformly coating said photoresist layer on said substrate, a base gas being introduced into said coater chamber to harden a surface of said photoresist layer; at least one vacuum-bake chamber connected to said coater chamber for heating said photoresist layer; a stepper chamber connected to said vacuum-bake chamber through an interface chamber, wherein said photoresist layer is exposed in said stepper chamber; and a developer chamber connected to said chill-plate chamber, wherein exposed or unexposed portion of said photoresist layer is removed in said developer chamber.
 10. The track system according to claim 9, wherein said base gas introduced into said coater chamber has a concentration between about 10⁻³ ppm and 10 mole/cm³.
 11. The track system according to claim 9, wherein said base gas has a pH value between about 7.1 and
 13. 12. The track system according to claim 9, wherein said base gas introduced into said coater chamber has a temperature between about 15 and 250 centigrade degrees.
 13. A deep ultra-violet (DUV) track system, said system comprises:an indexer end station for storing a substrate; a vapor-prime chamber connected to said indexer end station, wherein said substrate is heated and a chemical solution is applied on a surface of said substrate in said vapor-prime chamber before a photoresist layer is coated on said substrate; at least one chill-plate chamber connected to said vapor-prime chamber for bringing said substrate to a stable, constant temperature; a coater chamber connected to said chill-plate chamber for uniformly coating said photoresist layer on said substrate; at least one vacuum-bake chamber connected to said coater chamber for heating said photoresist layer, a base gas being introduced into said vacuum-bake chamber to harden a surface of said photoresist layer; a stepper chamber connected to said vacuum-bake chamber through an interface chamber, wherein said photoresist layer is exposed in said stepper chamber; and a developer chamber connected to said chill-plate chamber, wherein exposed or unexposed portion of said photoresist layer is removed in said developer chamber.
 14. The track system according to claim 13, wherein said base gas introduced into said vacuum-bake chamber has a concentration between about 10⁻³ ppm and 10 mole/cm³.
 15. The track system according to claim 13, wherein said base gas has a pH value between about 7.1 and
 13. 16. The track system according to claim 13, wherein said base gas introduced into said vacuum-bake chamber has a temperature between about 15 and 250 centigrade degrees.
 17. A deep ultra-violet (DUV) track system, said system comprises:an indexer end station for storing a substrate; a vapor-prime chamber connected to said indexer end station, wherein said substrate is heated and a chemical solution is applied on a surface of said substrate in said vapor-prime chamber before a photoresist layer is coated on said substrate; at least one chill-plate chamber connected to said vapor-prime chamber for bringing said substrate to a stable, constant temperature; a coater chamber connected to said chill-plate chamber for uniformly coating said photoresist layer on said substrate; at least one vacuum-bake chamber connected to said coater chamber for heating said photoresist layer; a stepper chamber connected to said vacuum-bake chamber through an interface chamber, wherein said photoresist layer is exposed in said stepper chamber, a base gas being introduced into said stepper chamber to harden a surface of said photoresist layer; and a developer chamber connected to said chill-plate chamber, wherein exposed or unexposed portion of said photoresist layer is removed in said developer chamber.
 18. The track system according to claim 17, wherein said base gas introduced into said stepper chamber has a concentration between about 10⁻³ ppm and 10 mole/cm³.
 19. The track system according to claim 17, wherein said base gas has a pH value between about 7.1 and
 13. 20. The process according to claim 17, wherein said base gas introduced into said stepper chamber has a temperature between about 15 and 250 centigrade degrees.
 21. A deep ultra-violet (DUV) track system, said system comprises:an indexer end station for storing a substrate; a vapor-prime chamber connected to said indexer end station, wherein said substrate is heated and a chemical solution is applied on a surface of said substrate in said vapor-prime chamber; at least one chill-plate chamber connected to said vapor-prime chamber for bringing said substrate to a stable, constant temperature; a coater chamber connected to said chill-plate chamber for uniformly coating said photoresist layer on said substrate; at least one vacuum-bake chamber connected to said coater chamber for heating said photoresist layer; a stepper chamber connected to said vacuum-bake chamber through an interface chamber, wherein said photoresist layer is exposed in said stepper chamber, a base gas being introduced into said interface chamber to harden a surface of said photoresist; and a developer chamber connected to said chill-plate chamber, wherein exposed or unexposed portion of said photoresist layer is removed in said developer chamber.
 22. The track system according to claim 21, wherein said base gas introduced into said interface chamber has a concentration between about 10⁻³ ppm and 10 mole/cm³.
 23. The track system according to claim 21, wherein said base gas has a pH value between about 7.1 and
 13. 24. The track system according to claim 21, wherein said base gas introduced into said interface chamber has a temperature between about 15 and 250 centigrade degrees. 